The present invention relates to apparatus for breaking up stacks of paper sheets or the like into smaller stacks or layers. More particularly, the invention relates to improvements in apparatus wherein successive stacks are broken up by a sword-like dividing member (hereinafter called sword for short) which penetrates into one edge face of a stack and thereby divides the stack into two layers.
Dividing apparatus of the above outlined character normally comprise a tongs or analogous means for gripping a stack in the region of the edge which is to be entered into by the sword. As a rule, one jaw of the tongs is adjustable substantially at right angles to the general plane of the dividing sword, and the other jaw of the tongs is biased by one or more springs or the like so as to yieldably bear against the adjacent outermost sheet or panel of the stack in the tongs. Furthermore, conventional dividing apparatus which embody the just discussed components further comprise conveyor means for removing successive smaller stacks or layers from the dividing station.
Dividing apparatus for stacks of paper sheets or the like are used in production lines for steno pads, brochures, note books and like commodities. Such apparatus are installed ahead of the stations for machines or apparatus which must receive stacks of predetermined thickness or which cannot process stacks whose thickness exceeds a predetermined value. Thus, if the machine or apparatus at the preceding station of the production line assembles or processes relatively thick stacks of overlapping panels or sheets, the next-following station must be preceded by an apparatus which can reduce the height of stacks to an acceptable value. A machine which cannot treat stacks having a thickness in excess of a given value is a punch which perforates successive stacks along one edge to provide holes for insertion of spiral binders or other means for movably coupling the sheets of a layer or stack to each other. The number of stages during subdivision of a relatively thick stack into thinner stacks or layers depends on the thickness of the original stack and on the desired or permissible thickness or height of the smaller stacks or layers. Thus, a relatively thick stack will have to be divided into more than two layers if the next following station can accept only relatively thin layers, i.e., layers whose maximum permissible thickness is less than one-half the thickness of the original stack. Furthermore, it happens again and again that the thickness of original stacks varies, even if the number of sheets or panels in each of a series of several stacks is the same. In order to take into consideration such unpredictable variations in the height or thickness of original stacks, it is often desirable to carry out the expected or anticipated number of dividing or breaking up operations plus an additional dividing operation to thereby insure that the height of each and every layer is invariably within the desired range. In other words, let it be assumed that the height of each of a series of successive stacks is a whole multiple, or close to a whole multiple, of the desired maximum height of a layer. Such stacks are subjected to n (instead of n-1) dividing operations (wherein n is the theoretical number of satisfactory layers which can be obtained from a stack) whereby the last or n-th dividing step is carried out for the sole purpose of insuring that the thickness of the last layer will not exceed the permissible maximum value. Similar results can be achieved by appropriate positioning of the adjustable jaw of the aforementioned tongs so that the thickness of each layer is less than the maximum permissible thickness. In such instances, too, a stack whose thickness matches or approximates a whole multiple of the maximum permissible thickness of a layer will be broken up into layers whose thickness is invariably acceptable for further processing at the next-following station of a production line for note books or the like. In the absence of such precautionary measures, the sword which, as a rule, is rigidly connected with the drive of the dividing apparatus or with the main prime mover of the production line, and which is moved back and forth in rhythm with the operation of other mobile parts, would be likely to penetrate into the last (normally the lowermost) layer of a stack whenever the thickness of such last layer exceeds the permissible value. This will be readily appreciated since the sword normally performs a stroke subsequent to separation of the penultimate layer from the last layer of a stack and before the dividing station receives a fresh stack. Such "superfluous" stroke of the sword is likely to result in deformation and/or other damage to one or more sheets of the last layer if the thickness of the last layer is excessive. Furthermore, and if the stack contains one or more relatively thick sheets (such as panels made of cardboard or the like and serving as covers for the upper sides and/or undersides of discrete layers), the sword is likely to penetrate into a panel. Similar situations can arise when the relatively thick panels are located at the top and the bottom of a stack which is to be subdivided into two or more thinner stacks or layers.
In order to avoid the above-outlined problems which are in part inherent in the presently known dividing apparatus, such apparatus are normally operated at less than maximum speed so that their output is relatively low. Thus, in order to insure that the sword and/or other parts of the dividing apparatus will not damage the sheets of the stacks and/or layers, the output of such apparatus is intentionally reduced in order to operate with a safety factor which is evidently undesirable, especially when the dividing apparatus form part of complete production lines which are set up for the express purpose of maximizing the output. In many production lines, the apparatus for breaking up stacks of paper sheets or the like constitute bottlenecks which limit the output of the entire production line because their operation is slower than necessary to insure the operation of the next-following machine or apparatus at maximum capacity.